Welcome! It depends on a lot.. I took one of a small 20 gallon tank because it just wasn't worth the space it took up. I did however have a strict water change schedule as well as plenty of oxygen exchange. PH stayed around 8.3.
Welcome and have fun! lots of great folks and resources here. As for an AIO and skimmer - i have an rsm130 and found the skimmer to be hit or miss with lots of fiddling. Like others i stick to water changes now but YMMV.